Abstract: A new motion compensation approach of ISAR is developed based on the frequency domain method of range realignment which is able to perform range realignment and phase compensation simultaneously. Consequently,the proposed approach can reduce the complexity and computational load of motion compensation of ISAR. It is proved that the scheme of phase compensation is virtually equivalent to the track Doppler centroid method. The proposed approach is used to process the live data of ISAR and the real data of microwave anechoic chamber. The results show that the proposed approach is correct and effective.